Jul 31, 1999

Farewell, Lunar Prospector

NASA's lunar orbiter crashed into the Moon Saturday, July 31, 1999, precisely striking its intended target


Lunar Prospector by Duane Hilton
July 31, 1999: Lunar Prospector, "the little spacecraft that could," can't anymore. As a room full of viewers and observatories from around the world looked on, the LP Mission Control team successfully ended the Lunar Prospector mission at 2:52:00.8 a.m. PDT on July 31 when the spacecraft slammed into a deep crater near the south pole of the moon.

Right: Artist Duane Hilton's rendering of NASA's Lunar Prospector spacecraft.

No visible debris plume was reported and it may be several days before data from ground- and space-based observatories and telescopes can be analyzed to determine if any water vapor was liberated by the impact.

For more science news and images from Lunar Prospector visit

Mission Control at NASA's Ames Research Center indicated that they are confident the small, spin-stabilized spacecraft hit its intended target precisely. The failure to reacquire a signal from the vehicle at the time it would have emerged from the dark side of the moon is proof that impact occurred. The absence of a visible debris plume is not a negative result. In fact, it increases the likelihood that the spacecraft impacted deep into the intended target crater.

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The final sequence of events for Prospector began at 1:17 a.m. PDT when the Mission Control team successfully loaded a 60-minute pre-programmed countdown into Prospector's internal clock to initiate the final burn sequence. At 2:00 a.m. PDT, final loss of signal from Prospector occurred, as planned, when the spacecraft passed behind the moon for the last time. Alan Binder, Lunar Prospector Principal Investigator observed, "we don't want to hear from Prospector again - if we do, we've missed our mark." He was not to be disappointed.

The scheduled 4 minute 36.5 second burn was executed behind the moon at 2:17 a.m. "Prospector's engines should be burning full -- preparing to de-orbit," said Binder. "It is now hurtling towards its destiny at approximately 1.7 kilometers per second on a ballistic trajectory that will take it to its target crater."

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The spacecraft's key scientific instruments continued to send data until the very end when signal was lost. "Once again, Prospector has done everything we have asked of it," said Binder. "This mission provided ten times better data than we expected. The spacecraft performed flawlessly to its very end. Scientists will be analyzing the tremendous volume of valuable data obtained for years to come," he concluded.

Analysis of data obtained during the mission-end experiment will be ongoing for days, and possibly weeks, to come. At the completion of that analysis, scientists will have a much better idea if Prospector has, in fact, provided the definitive evidence of water ice on the moon that they were seeking. A positive result may have the potential to open up expanded possibilities for solar system exploration. Failure to prove conclusively that water ice exists in the lunar polar regions by no means suggests that it is absent, according to mission scientists. It simply means that this particular bold experiment, acknowledged as high payoff but also with low probability of success, has not provided the conclusive evidence that was being sought.

Please visit the Lunar Prospector project web site from NASA/Ames and the Lunar Prospector impact page from UT Austin for more information about Lunar Prospector's crash into the Moon. See also: for more science news and images.

Lunar Prospector was the first of NASA's competitively selected "faster, better, cheaper" Discovery-class missions. The $63 million mission is managed by NASA Ames Research Center, Moffett Field, CA.

Web Links

Lunar Prospector in Eclipse -- The July 28, 1999 partial lunar eclipse poses a last-minute threat to Lunar Prospector. , July 28, 1999, NASA Space Science News

Bracing for Impact -- Astronomers prepare to observe the crash of Lunar Prospector on July 31, 1999. Includes observing hints for amateurs, July 21, 1999, NASA Science News

Destined for a Watery Grave -- NASA scientists have decided to send Lunar Prospector crashing into the Moon's south pole in search of water, June 4, 1999, NASA Science News

Zeroing in on Lunar Ice -- Astronomers explore the Lunar Prospector crash site using radar, June 4, 1999, NASA Space Science News

Lunar Prospector set to make science "splash" -- NASA/Ames press release

NASA Press Release (3 September 1998) -- announcing enhanced estimate of quantity of water on the Moon

NASA Press Release (5 March 1998) -- announcing the detection of ice on the Moon

Lunar Prospector Home Page -- from NASA/Ames

Ice on the Moon -- informative article about lunar water -- where it is and how to find it.

Lunar Prospects -- Astronomy Picture of the Day, Sep. 18, 1998

Impact Moon -- Astronomy Picture of the Day, Mar. 26, 1999

The Nine Planets: the Moon -- from SEDS

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